Materials mixing rotors with standard threads, configured as depicted in prior art FIGS. 1 and 2, were seen to be breaking down, and would not run for more than a few weeks, causing down time and requiring major rotor construction, if salvageable. Such prior art rotors were wrapping molten materials about their periphery, creating pinch points, that caused the elongate rotor pairs to deflect. Such repetitive deflection eventually caused rotor cracking, and operational breakdown. Thus, the standard threaded rotor was structurally weakened and gave only limited and costly operational longevity when using standard threads on flights throughout the mixing length.
According to the present invention, an alternative configuration for the peripheral threads was devised, whereby a second and distinct set (flight) of threads were provided by adding to the threads span, and by abutting the opposite helixes, so as to help the flow of material to the helix segments of the rotors. The second flight comprises a set of Lowenherz threads, adapted to make the rotors stronger, by adding a sloped radius to the threads of the added second flight. Such will also serve to cut and churn the multi-materials being fed to the materials mixer.
The dual flight rotors of the present invention have typically operated for extended periods, without rotor flexing and associated cracking, calling only for infrequent shutdowns to change the composition of the polymer materials being processed.
Accordingly, it is a principal object of the present invention to provide a rotor assembly that avoids jamming up from fluidized partial bottom feeds so as to extend the operational range for a given sealing means and paired rotor assembly.
Another object of the invention is to modify the standard flight configuration to include a separate flight of threads, each having a linear bevel on the upstream stage for one of the flights, whereby more uniform cutting and churning of the particulate feed materials is accomplished.
It is another object of the present invention to increase the root diameter of the mixing rotor significantly, which serves to increase its structural strength and obviates its flexing from materials binding with it during processing.
A still further object of the invention is to provide improved means for the interconnection of the drive shaft and mixing rotor by adding to the drive surface provided at each longitudinal end of the rotor itself with a special keying means.
Yet another of the invention is to preclude operational failures of the mixing assembly caused by deflection of the rotor under materials compression during the vigorous mixing phase.